effect of engine knocking

Hello there,

I'm a little confused, i've heard cases of an engine running too lean and you get pinging untill you've readjusted the mixture. I've also heard stories of engines being run on dyno and the engine blows a hole in the block because it ran too lean and detonated. Someone pls be kind enough to clear this up with me.

Thanks.

Reply to
Brian Su
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The mixture burns when it wants to, and in a more explosive rather than smooth fashion AFAIK. The mixture could burn while the piston is still on the way back up in the compression stroke, which would be an extra bad thing I suppose. I've not heard of anyone blowing a hole in the block, but plenty of tales of pistons getting holes knocked through them. Have a look on the google groups archives, Ed with the turbo micra lost a piston to detonation a while back and posted pictures.

Reply to
Doki

pinking is when you have the engine running lean pre-ignition is when the engine has run so hot it causes the mixture to burn before it hits the correct point BTDC the ignition spark sets of a controlled burn the others create an explosion which shocks the piston in the bore which leads to the telltale "pink" on a dyno this pink shows up as a cloud of soot coming out the exhaust where the old carbon deposits are shaken loose from the combustion chamber

either way, it's bad for engines if it happens

the cause of engines blowing up on dyno's is more a case of not enough fuel and too high a rev most cars will happily supply enough fuel for top end cruising up till the red line after this you don't get enough fuel going into the system on the road this is easily cured because you can't DO a red line on the car because it's just not going to have the grunt to do it, but on the rollers, when youdon't have wind resistance (and it's also in 4th and not fifth) the extended exposure to top end engine speeds tends to lean out the fuel and this tends to cook engines

at least that's what I've been told when I blew my engine up ;)

Reply to
dojj

Pinking is when it detonates due to exess heat, too much carbon build up (compression) crap low octane fuel, weak mixture, spark too advanced at thias point. Or any combination of the above. Retarding the ignition 2 degrees normally will stop it, because the detonation happens because the fuel detonates as the pressure rise is too fast. So it begins to burn then expands and this increases the burn speed which in turn causes it to expand faster etc etc. Then bang...

Or a part of it like a plug electrode, badly seating valve, or a lump of carbon... Which then (can) cause it to detonate!

???? What about 3rd 4th, or down hills?

Err no. I spent years with dynos and engines. Not the case. All of this depends on so many variables that its not possible to generalise!

If the fuel system was "innadequate" as fas as supply volume was concerned then it would go weak at peak power, not at the redline as less fuel is required here...

They were dummies!

Reply to
Burgerman

but thats what i've explained as pre igniton ;)

when you are in 5th, you travel a lot faster for longer periods of time this shows up the weak point in the system beacuse youwill run out fo fuel because it takes longer to reach the redline than it does inthe other gears this is also the reason so many cars blow up when they do top speed runs, they don't have sufficent fueling to DO the run even if the car has been mapped and stuff on the dyno because dyno runs don't take this sort of situation into the equation cossie tuners (for a guide) rekcon that about 400 brake is th elimit of the standard fuel pump system after that you have to switch to either twin pumps of group A spec (whatever that is)

it's hard to explain, but i'll try to put my sideof the arguement here first gear is over and done with before you have a chance to do anything the fueling is great because, even when you are running at the top end, you aren't running there for very long so it doesn't have a chance to run lean at the top end when you need to be getting enough fuel to make the power you need to make @ 7k rpm (just as an exapmle) second is a little longer as is third as is forth as is fifth now imagine that youcan't sustain the fule delivery at the top of the rev range due to it not having enough "pump" to supply the fuel needed to make the power at that engine speed as it's been running there for longer than the dyno run has had it there for beleive me, it all makes sense when you put it as power = boost but you can't make the fueling to keep the boost i can't explain it better than that :)

well, no alomst at full chat boost was at the top ignition was sorted ignition wire came off fueling went back to normal ignition went back to normal there was no way that i was going to see 300+ bhp and 12 psi with the igniton thinking it was only set for 177 and atmospheric :)

Reply to
dojj

The fuel system has no idea how fast you are going!!!

If it fuels correctly for 5 secs at max power then it will continue to do so. There is no "float bowl" or anything to run out so to speak, its all just dynamic instant fuel flow and pressures with fuel injection.

With a carb and a float bowl this could be the case. Not with constant regulated fuel pressures. Because time is not one of the variables. If the opump can flow enough to correctly fuel something at peak power for a second or so it can do so continuously. There is no "reserve" so to speak.

Only if they are not set correctly in the first place. This is not a "fuel pump too small" problem Or it would have run weak at full power on the dyno too.

? Err yes. They do. Why does the pump suddenly start to flow less during a long flat out run? It doesent.

This is not relevant - only to that particular car. And if 400 is the limit it would be the limit on a dyno set up run or a top speed run as well. So it tells you nothing.

I used to build both dynos and race engines as well as nitrous systems and used to do power runs in any gear I felt like!

?????????????????? Ehhh ONLY if not set up correctly. Actually most production vehicles and especially bikes are set up to go overly RICH at very high rpms, as an atempt to knock off power a bit earlier to stop people "hanging on" to gears too long etc...

Yes it does. You just don't have chance to a) feel it! b) damage anything...

Then it would be weak at this engine speed (peak power NOT redline) in ALL gears anyway! Its just that YOU cant detect it and the damage has not occured because there was no time to heat things up...

And this may be a fuel mapping error, an ignition mapping error, or an incorrectly sized pump. But if all this is correct then it does not matter how long you stay at full power for.

You are confused I think. The reason that top speed runs usually kills an otherwise fit engines that the stress goes on for longer and heat soak into the internals, oil, cooling system etc causes detonation, or gasket faliure, or starts the onset of detonation that the continued WOT helps to continue to the death.

This MAY have been caused by the fuel pump not being man enough, (along with any one of 100 different reasons) but the incorrect fueling SHOULD have been noticed on the dyno even during a short run. Then it would not have caused a problem later on during a top speed run...

Incidentally, on most engines the redline is way past peak power (My 1200 bandit for eg has peak power at 8750rpm but 11,000 red line.) So the greatest fuel requirement was at 8750 not the rev limiter...

Then it wasn't the fuel pump???

Reply to
Burgerman

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